1. The Field of the Invention
The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention is directed to a method for performing a selective hydrofluoric acid (HF) based etch which method is useful in the formation of spacers and other structures of silicon dioxide during the manufacture of semiconductor devices.
2. The Relevant Technology
In the continuing quest to reduce the minimum feature size in integrated circuits, anisotropic plasma etching has found wide application, including for example its use in forming trenches in a silicon substrate for device isolation and for cell capacitor structures in DRAM designs, for defining polysilicon gates, for etching contacts and vias, and for forming spacers. Ion bombardment is used to increase the reaction rate in the direction of the bombardment, and film forming agents are used to decrease or prevent reactions on non-bombarded surfaces, resulting in a highly directional etch.
One drawback of plasma etching is its limited selectivity relative to chemically selective etches. A wet etch, vapor etch, or anhydrous etch of silicon dioxide in HF, for example, can achieve nearly infinite selectivity to silicon. Plasma etches are currently limited to 15:1, 20:1, or at most 30:1 selectivity. Selectivity to silicon is particularly useful in the formation of spacers, during which a layer of silicon oxide is typically removed from a source/drain area of the substrate. The source/drain area is particularly sensitive to damage caused by ion bombardment. If the source/drain area is significantly etched, an adjacent gate may be damaged and reliable contacts to the source/drain area may be difficult to form. A method of forming spacers with an HF based chemically selective etch process would prevent any damage to the source/drain area and is thus highly desirable.